Folding shoe for use in a packaging machine

ABSTRACT

Flexible sheet material made of plastic, paper, metal foil, or the like is pulled off of a supply roll and passed over and through the folding shoe for forming packages or bags for holding various types of products. In one embodiment, the folding shoe includes a truncated tubular portion and a skirt portion surrounding such tubular portion and joined to the inclined throat formed by the truncated end thereof. Such skirt portion includes a sloping tail section extending outwardly from the high side of the throat for guiding the sheet material thereto. Such sheet material is then pulled downwardly through the throat and the tubular portion to fold it into a tubular form having an overlapping seam which is sealed as the tubular form leaves the folding shoe. After sealing the tubular form in a transverse or crosswise manner, the desired product can be loaded into the resulting tubular package by way of the passage through the tubular portion of the folding shoe, after which the package is transversely sealed above the product load and cut or severed from the folded sheet material then emerging from the folding shoe. In another embodiment, the tubular portion of the folding shoe is omitted and only the skirt portion is used. In a further embodiment, most of the skirt portion is omitted, only the outer part of the tail section being used, such part being held in a spaced-apart relationship with respect to the tubular portion. In any of these various embodiments, the folding throat can be shaped to fold the sheet material into either a round or an obround or a flat form.

United States Patent Bowen et al.

I 54] FOLDING SHOE FOR USE IN A PACKAGING MACHINE [72] lnventors: Burlie R. Bowen; William L. Heemer, Jr., both of 0/0 General Packaging Equipment Co. PO. Box i9525, Houston, Tex. 77024 [22] Filed: Oct. 24, 1969 [21] Appl.No.: 869,224

[52] 0.8. CI. ..93/59 R, 53/180, 93/82, 1 13/ l 16 UT [51] Int. Cl. ..B3lb 1/42, B65b 9/00 [58] Field ofSearch ..93/59, 82; 53/28, 180, I82

[56] References Cited UNITED STATES PATENTS 3,326,097 6/1967 Lokey ..93/82 3,432,980 3/!969 Seiferth et al ..53/182 X 3,494,265 2/1970 Middour ..93/82 Primary Examiner-Theron E. Condon Assistant Examiner-Neil Abrams Attorney-Jack W. Hayden 1 Jan. 25, 1972 7 1 ABSTRACT Flexible sheet material made of plastic, paper, metal foil, or the like is pulled off of a supply roll and passed over and through the folding shoe for forming packages or bags for holding various types of products. In one embodiment, the folding shoe includes a truncated tubular portion and a skirt portion surrounding such tubular portion and joined to the inclined throat formed by the truncated end thereof. Such skirt portion includes a sloping tail section extending outwardly from the high side of the throat for guiding the sheet material thereto. Such sheet material is then pulled downwardly through the throat and the tubular portion to fold it into a tubular form having an overlapping seam which is sealed as the tubular form leaves the folding shoe. After sealing the tubular form in a transverse or crosswise manner, the desired product can be loaded into the resulting tubular package by way of the passage through the tubular portion of the folding shoe, after which the package is transversely sealed above the product load and cut or severed from the folded sheet material then emerging from the folding shoe.

In another embodiment, the tubular portion of the folding shoe is omitted and only the skirt portion is used. ln a further embodiment, most of the skirt portion is omitted, only the outer part of the tail section being used, such part being held in a spaced-apart relationship with respect to the tubular portion. In any of these various embodiments, the folding throat can be shaped to fold the sheet material into either a round or an obround or a flat form.

35 Claims, 14 Drawing Figures PATENTED JAHZS r912 SHEET 2 0F 5 lNl ENTURJ Jada Magda] pichauui 6- Bee,

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FOLDING SHOE FOR USE IN A PACKAGING MACHINE BACKGROUND OF THE INVENTION This invention relates to folding shoes for use in packaging machines for making packages or bags from a continuous web of flexible sheet material and to methods of fabricating such folding shoes.

Automatic packaging machines are presently used for automatically placing various types of goods and products into sealed plastic or paper or foil bags. Typical products which are packaged in this manner are potato chips, cookies, popcorn, rice, sliced meats, dill pickles, vegetables, fertilizers, cement, metal parts and many and various other types of dry and liquid goods. The packaging machine forms the packages or bags and fills them with the desired quantity of the product all in one continuous operation.

A representative present-day packaging machine is described in US. Pat. No. 3,070,931, granted to Daniel H. Zwight on J an. 1, 1963. As there described, a continuous web of flexible packaging material is pulled over and through a forming device or folding shoe for folding the packaging material into a tubular shape having an overlapping seam. A longitudinal heat sealer located downstream of the folding shoe seals the seam as the tubular material moves therepast. A transverse heat sealer carried by a material gripping pulldown device forms a transverse heat seal crosswise of the tubular material. This forms the bottom of a package. At this point, a selected quantity of the product to be packaged is dumped into the tube of packaging material by way of the tube-forming passage in the folding shoe. At this point, the pulldown device opens up so as to become disengaged from the package. Such device is then moved upwardly to a point above the product load, whereupon it is again closed and a transverse heat sealer carried thereby is operated to form a second transverse heat seal crosswise of the tubular packaging material to thus form the top of the package. A cutting knife in the pulldown device is then operated to sever the completed package from the pulldown device. The pulldown device, which is still in a closed condition, then moves in a downwardly direction to pull a new length of tubular packaging material into position for loading.

The packaging machine described in the Zwight patent works in a very satisfactory manner. A problem exists, however, in that the folding shoe described therein is rather difficult to fabricate. Its shape and dimensions are critical. If such factors are not just right, to within a fairly close tolerance, then the packaging material may be wrinkled or scratched or broken as it is pulled over and through the folding shoe. Heretofore, such folding shoes have been fabricated in a largely manual manner with their final shape being arrived at on a trial and error basis. The shoe is first put together on an intuitive basis and then tested to see what happens. The shoe is then modified in an attempt to eliminate any undesired effects. After this, it is again tested to see what happens and any necessary further modifications are made. This process is repeated until a shape is finally obtained which produces an acceptable quality for the resulting packages.

Needless to say, this trial and error method is usually rather time consuming and not very economical. The importance of this can be better appreciated when it is realized that the life of a folding shoe is limited and a replacement is sooner or later needed. Also, difierent types of products require different sizes and shapes of folding shoes. Thus, it is difficult to keep up with the demand for such folding shoes using the existing trial and error approach.

SUMMARY OF THE INVENTION It is an object of the invention, therefore, to provide a new and improved folding shoe for use in a packaging machine and which is easier and more economical to fabricate.

It is another object of the invention to provide a new and improved method of fabricating folding shoes which eliminates the trial and error steps of the methods presently in use.

It is a further object of the invention to provide a new and improved method of fabricating folding shoes which enables a variety of different sizes and shapes of folding shoes to be fabricated in an economical, efficient and straightforward manner.

It is an additional object of the invention to provide a new and improved folding shoe for providing a very smooth and scratch-free folding operation in a packaging machine.

It is a further object of the invention to provide a new and improved folding shoe for folding fragile types of packaging materials without scratching or breaking same.

In accordance with the invention, there is provided a folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape. The folding shoe includes a guide surface for initially receiving the sheet material and guiding it in a first direction. The folding shoe also includes means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction, at least a portion of such throat being inclined relative to this second direction.

In accordance with one feature of the invention, the throat is shaped such that if the throat means is split at the low point of the throat and unfolded so that the throat line lies in a single plane, such throat line would describe an arched line extending from and returning to a baseline passing through the end points of such throat line with such arched line being symmetrical about a line perpendicular to the baseline and passing through the midpoint of the arched line. Such arched line includes linear segments extending upwardly from the baseline and inclined inwardly towards the midpoint and parabolic segments extending from the upper ends of the linear segments and curving inwardly towards the midpoint.

In accordance with another feature of the invention, the length of the throat, as measured along an axis running parallel to the second direction, is equal to T3109 inches where T is defined by the relationship:

T=0.738 WO.238F where Wis the width of the tube when pressed flat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

In accordance with a further feature of the invention, the distance from the far edge of the guide surface to the near edge of the throat, as measured along a line running perpendicular to the second direction, is equal to G- '-l 0% where G is defined by the relationship:

G=1.024W+l.036L-H).0l3F where W is the width of the tube when pressed flat, L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

For a better understanding of the present invention, together with other and further objects and features thereof, reference is had to the following description taken in connection with the accompanying drawings, the scope of the invention being pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings:

FIG. 1 is a plan view of a first embodiment of a folding shoe constructed in accordance with the present invention for folding packaging material into an obround tube;

FIG. 2 is a cross-sectional view taken along section line 2- 2 of FIG. 1;

FIG. 3 is a partial front elevational view of the obround folding shoe of FIG. I;

FIG. 4 is a perspective view of the obround folding shoe of FIG. 1;

FIG. 5 illustrates in a somewhat diagrammatic manner a cross-sectional view of the tube produced by the FIG. 1 folding shoe when such tube is pressed flat;

FIG. 6 is an unfolded or developed view of the obround folding shoe of FIG. 1;

FIG. 7 is an unfolded or developed view of a second embodiment of a folding shoe constructed in accordance with the present invention for folding packaging material into a round tube;

FIG. 8 is a side elevational view of the round folding shoe obtained with the unfolded pattern of FIG. 7;

FIG. 9 is a plan view of the round folding shoe of FIG. 8;

FIG. 10 is a side elevational view of a skirtless embodiment of a folding shoe constructed in accordance with the present invention;

FIG. 11 is a plan view of the skirtless folding shoe of FIG. 10;

FIG. 12 is a cross-sectional view of a tubeless embodiment of a folding shoe constructed in accordance with the present invention;

FIG. 13 is an unfolded view of yet another embodiment of a folding shoe constructed in accordance with the present invention for folding packaging material into a flat tube; and

FIG. 14 is a perspective view of the flat folding shoe obtained with the unfolded pattern of FIG. 13.

DESCRIPTION OF THE OBROUND EMBODIMENT OF FIGS. 16

FIGS. 1-4 show different views of a folding shoe for use in folding flexible sheet material into a tube on obround shape. The folding shoe 20 includes a truncated tubular member 21 having the opening at the truncated end thereof inclined relative to the longitudinal center axis of such tubular member 21 to provide a downwardly curving throat 22 for receiving and folding the packaging material. As indicated in FIG. 1, the base of the tubular member 21 is of obround shape. As such, the tubular member 21 includes a first flat side 23, a pair of semicircular ends 24 and 25 and a second flat side formed by overlapping side pieces 26a and 2617. Thus, the tubular member 21 is split and overlapped at the low point of the throat 22. The width of the overlap is designated as L. Though not readily visible in FIG. 1, the overlapped ends of sidepieces 26a and 26b are separated by a small gap for enabling the passage of packaging material therebetween. As indicated in FIG. 2, the tubular member 21 is carried by a support plate 27 having an obround hole 27a formed at one end thereof for receiving a lower extension 28 of the tubular member 21. As indicated in FIGS. I and 2, the hole 27a includes a recessed slot 27b located in front of the overlapping ends of members 26a and 26b and extending through the support plate 27 from the top to the bottom thereof.

The folding shoe 20 further includes a skirt member 30 surrounding the tubular member 21 and joined to the inclined throat 22. Such skirt member 30 includes a sloping, outwardly flaring tail section extending outwardly from the high side of the throat 22 for guiding the packaging material thereto. More particularly, the skirt member 30 includes a first or upper flat tail surface 31 joined to the high side of the throat 22 and extending outwardly from the tubular member 21 in a downwardly direction. The skirt member 30 further includes a second or lower flat tail surface 32 joined to the outer extremity of the upper tail surface 31 and extending outwardly from the tubular member 21 in a downwardly direction but at a different angle relative to the longitudinal axis of the tubular member 21. As seen in the plan view of FIG. 1, both the upper tail surface 31 and the lower tail surface 32 are of trapezoidal shape with the longer of the two parallel edges in each case being located at the greater distance from the tubular member 21. As will be seen, the leading or outermost edge 33 of the lower tail surface 32 is perpendicular to the direction of movement of the packaging material and the length of such edge 33 is equal to the width of such packaging or sheet material. Lower tail surface 32 further includes side edges 34 and 35 (FIG. 4) which form acute angles with respect to the leading edge 33.

The skirt member 30 further includes a pair of flat side surfaces 36 (FIG. 4) and 37 (not visible) which extend vertically and which run from the side edges 34 and 35 of the lower tail surface 32 to the tubular member 21..The exact shape of these side surfaces 36 and 37 will be better seen in connection with an unfolded view to be considered hereinafter. The planes of these flat side surfaces 36 and 37 are parallel to the longitudinal axis of the tubular member 21, which axis is vertical for the particular orientation shown in the drawings. These side surfaces 36 and 37 are tangent to the curvature of the tubular member 21 along the lines of contact therewith. A pair of curved shoulder surfaces 38 and 39 extend over the two remaining areas bounded by the two flat side surfaces 36 and 37, the side edges of the upper tail surface 31 and the edge of throat 22. As indicated in the perspective view of FIG. 4, the skirt member 30 has a smooth appearance with the various curved surfaces thereof blending into the adjacent flat surfaces in a smooth and continuous manner.

The edge of the throat 22 is somewhat rounded in the direction of movement of the packaging material thereover. It is not a sharp knife edge. The radius of such curvature may be on the order of, for example, one or two thousandths of an inch.

As seen in FIG. 2, the skirt member 30 is also carried by the support plate 27. As previously mentioned, such skirt member 30 isjoined to the throat 22 of the tubular member 21. In addition, the skirt member 30 includes an inwardly extending flap 40 which is bolted to the support plate 27 by suitable nuts and bolts 41 and 42. As seen in FIG. 1, the skirt member 30 is further provided with a pair of outwardly extending tabs 43 and 44 which are also bolted to the support plate 27. In use, support plate 27 is bolted to or otherwise mounted on the packaging machine proper.

There is shown in outline form in FIG. 2 certain of the principal parts of the packaging machine itself. A roll of the flat sheetlike packaging material to be folded is indicated at 45. The packaging or sheet material being pulled off the roll 45 is indicated at 46. Such sheet material 46 is relatively thin and flexible and may be made of plastic, paper, metal foil, or any other material suitable for packaging or wrapping purposes. The packaging or sheet material 46 is pulled off the supply roll 45 and up the inclined tail surfaces 32 and 31. It is then pulled downwardly through the interior of the tubular member 21 and out the bottom thereof. The shape of the throat 22 is such that the sheet material 46 is folded into a tubular form as indicated at 460. In this regard, it should also be noted that the sheet material 46 is being pulled along the flat side surfaces 36 and 37 (FIG. 4) and the curved shoulder surfaces 38 and 39, as well as along the tail surfaces 31 and 32. In other words, for the particular construction shown in FIGS. 1-4, the outside of the skirt member 30 is completely covered with the sheet material 46 as such material is being pulled through the tubular member 21. For example and looking at FIG. 4, the righthand side portion of the sheet material 46 (looking downstream) moves along the flat sidewall 36, around the bend and along the flat piece 26b located on the front side of the tubular member 21. Such side portion of the sheet material 46 is then folded over the part of the throat 22 formed by the upper edge of the frontpiece 26b. As a consequence, the sheet material 46 is folded into a tubular shape corresponding to the shape of the base of the tubular member 21. In the present embodiment, this shape is of an obround nature.

Because of the dimensions of the tubular member 21, the folding is such that the sheet material 46 is overlapped on the side of the tube 460 on which are located the frontpieces 26a and 26b. The width of the overlap is the same as the width of the overlap of the frontpieces 26a and 26b. As the packaging tube 46a emerges from the tubular member 21. the overlapping seam is heat sealed by a vertical heat sealer indicated in outline form at 47. A backup plate 48, located inside of the packaging tube 46a. cooperates with the heat sealer 47 for forming the seal. Backup plate 48 is held in the desired position by means of a mounting member 480. An appropriate pulldown device for pulling the packaging material 46 through the tubular member .21 is located below the heat sealer 47.

Such device is not shown herein and may, for example, take the form of the pulldown device described in the above referred to US. Pat. No. 3,070,931 to Zwight. A loading funnel 49 extends part way into the upper end of the tubular member 21 and is used for purposes of feeding the product to be packaged into the tube of packaging material 46a at appropriate intervals.

Referring now to FIG. 5, there is represented a cross-sectional view of the tube of packaging material 460 when such tube is pressed flat. This pressing flat occurs when the transverse or crosswise seams forming the top and bottom of the package are made. The overlapping vertical seam in the packaging material is indicated at 46b. As is further indicated, the overall width W of the resulting package is determined by the width F of the flat-sided portion 23 of the tubular member 21 and the radius of curvature r of the curved side portions 24 and 25 of the tubular member 21. In particular, for the obround case, W is described by the relationship:

W=1TI+F 1 This is a basic relationship which relates the parameters r and F of the folding shoe to the desired width of the bag or package to be formed.

A principal advantage of the present invention is the ease and economy with which folding shoes made in accordance therewith may be fabricated. In particular, an appropriate pattern can be laid out on a flat piece of sheet metal and the sheet metal then folded along the appropriate lines to produce the desired folding shoe. Not only is this relatively quick and simple to do, but of at least equal importance is the fact that the resulting folding shoe is of just exactly the right size and shape. No trial and error testing and modifying of the folding shoe are required.

Returning to the particulars of the FIGS. 1-4 embodiment, the folding shoe 20 is made from a single piece of sheet metal which is folded in the proper manner. An unfolded or developed view of this piece of sheet metal is indicated at 50 in FIG. 6. The sheet metal 50 may be, for example, stainless steel having a thickness in the range of, for example, 0.0239 to 0.0359 inches (24 gauge to 20 gauge). The principal areas and edge lines on the unfolded sheet of FIG. 6 are, for ease of comparison, identified by the same reference numerals as used in FIGS. l-4. As seen in FIG. 6, the throat 22, when split at its low point 22a (FIG. 3) and unfolded so as to lie in a single plane, describes an arched line extending from and returning to a baseline passing through the end points of such throat line. Because of the presence of the overlap in the tubular member 21, care must be exercised in the explanation of what is meant by the end points and baseline for the throat 22. In terms of FIG. 6, the end points of the throat 22 are indicated at points 51 and 52, the baseline for the throat being indicated at 53. This set of definitions enables a discussion of the throat line 22 independently of the presence or absence or extent of the overlap. The midpoint of the arched throat line 22 in FIG. 6 is indicated at 54.

For purposes of explaining the layout of the lines on the flat sheet 50, it is convenient and orderly to think in terms of a set of X and Y coordinate axes. In the present explanation, the X axis is selected as being a line 55 running parallel to the throat baseline 53 and denoting the boundary between the principal rectangular area of the sheet 50 and the tubular extension portion 28. In this regard, the principal rectangular area is considered as being the rectangle which is left over when the tubular extension 28, the back flap 40, and the side tabs 43 and 44 are omitted. The Y coordinate axis for FIG. 6 is taken as being a line 56 which is perpendicular to the X axis 55 and which passes through the midpoint 54 of the arched throat line 22. The origin of the X and Y axes is at point 57. The spacing between the throat baseline 53 and the X coordinate axis 55 is dependent upon the width of the overlap and, in particular, is equal to one-half of such overlap width.

The construction of the throat line 22 is critical and will be described in detail. In particular, the unfolded throat line 22 of FIG. 6 is symmetrical about the Y axis 56 and includes linear segments 22b and 220 which extend upwardly from the baseline 53 and which are inclined inwardly towards the midpoint 54. The angle 0 between each of these linear segments 22b and 22c and the baseline 53 is equal to 45. Because of the presence of the overlap, the linear segments 22b and 22c are, in fact, also extended downwardly to the corresponding corners of the metal sheet 50. Thus, in terms of the X axis 55, the linear line segment 22b lies between X coordinate points LI and L2. Linear segment 22c, on the other hand, lies between X coordinate points L5 and L6.

The equation for the linear segment 22b is:

Y=X+W+0.5L The equation for the linear segment 22c is:

Y=X+W+0.5L The locations of the X axis points L1 and L6 are:

Ll=(W+0.5L) 4 L6=+( W+0.5L) s The unfolded throat line 22 of FIG. 6 further includes parabolic segments 22d and 22e extending from the upper ends of the linear segments 22b and 22c, respectively, and curving inwardly toward the midpoint 54. Parabolic segment 22d lies between X coordinate points L2 and L3, while parabolic segment 22e lies between X coordinate points L4 and L5. The location of these X axis points are as follows:

L2=(0.64308W0.14308F) L3=0.5F L4=+0.5F a L5=+(0.64308W0.l4308F) (9 With respect to the X and Y coordinate axes, the parabolic segment 22d is described by the equation:

where the exponential quantity (X+O.5F) is positive for all negative valves of X.

The equation describing the parabolic segment 22e with respect to the X and Y coordinate axes is:

+0.73806W0.23806F+9.5L (11 Several useful observations can now be made concerning the unfolded throat line 22. For one thing, the slope of the parabolic segment 22d at the point where it joins the linear segment 22b is equal to the slope of such linear segment 22b, such slope being equal to +1. Furthermore, the slope of the parabolic segment 22d at the point where it joins the linear segment 22f is equal to the slope of such linear segment 22f, such slope having a value at this point of zero. Similar considerations apply to the other parabolic segment 22e, except that the slope of its joining linear segment 22c is -l. A further useful observation is that the foregoing equations describing the various throat segments can, if desired, be referenced to the throat baseline 53, instead of the X axis line 55, by omitting the L terms from such equations.

In order for a proper functioning folding shoe to be obtained, the various points on the throat curve 22, after the metal sheet 50 is folded, must be located to within :009 inches of their correct locations.

The boundary lines separating the other principal surface areas on the metal sheet 50 are straight lines, the dimensions and locations of which are described by the parameters set forth in the following table. In addition thereto, this table is intended as a summary listing of all the various parameters represented by letters of the alphabet.

PARAMETER AND VALUE DESCRIPTION A=W+0.5L Half unfolded shoe width. B=l .5053 (HF) Lower tail length. C=ZW+L Unfolded shoe width. D=2W+l.6505L-O.34948F Unfolded shoe length. E=0.5L+e Tube extension cutback.

e=a constant (2. 0.25 inches) F=a design variable G=l.0236W+l.0362L+0.0l26F Tube flat width.

Horizontal component of the total tail length.

Minor axis tube width.

J=0.5L+0.5F Tail break height. K=0.73806W+0.5L0.23806F Tube length.

[Fa design variable Package lap width. M=O.SF Half Ilat width.

Half parabola width.

Upper tail length.

As seen from this table, the primary independent variables are W, L, and F. These variables are determined by the size and shape of package which it is desired to make and the extent of the desired overlap. Thus, once the package parameters are decided upon, the necessary pattern can be laid out on a flat sheet of metal and the metal then folded to provide the appropriate folding shoe.

In order to facilitate the proper folding of the metal sheet 50, some of the lines laid out thereon should be scored or undercut on the bottom side thereof. The lines which should be undercut are the arched throat line 22, the lower tail side edge lines 34 and 3S, and the tail break line 58 between the two tail surfaces 31 and 32.

DESCRIPTION OF THE ROUND EMBODIMENT OF FIGS. 7-9

FIGS. 7-9 show different views of a folding shoe 60 for use in folding flexible sheet material into a tube of round shape. As in the earlier obround embodiment, the shoe 60 is folded from the flat piece of sheet metal which has been properly cut and scored. FIGS. 8 and 9 show the final shape of the shoe 60 after it is folded, while FIG. 7 shows the flat metal sheet 61 from which the shoe 60 is obtained. As indicated in FIGS. 8

and 9, the folding shoe 60 includes a vertically extending tubular member 62 and a surrounding and rearwardly extending sloping skirt member 63. The throat of the tubular member 62 isindicated at 64 in FIG. 8.

A comparison of FIG. 9 with FIG. 1 shows that the principal difference in the present round embodiment is that the base of the tubular member 62 is now of circular or round shape. There is no flat-sided portion corresponding to the dimension F of FIG. 1. The F factor is now zero. The various equations and relationships set forth above also apply to the FIGS. 7-9 embodiment, provided that the factor F is set to zero in any of such equations and relationships in which it may appear. Thus, the same alphabetical designations for the various dimensions are used in the present round embodiment as were used in the earlier obround embodiment.

Apart from the round shape of the tubular member 62, the only other major difference is that the length B of the lower tail surface 65 is substantially less than that of the lower tail surface in the earlier obround embodiment. In the present round embodiment, such length B is controlled only by the width of overlap (L) which is desired for the resultant package.

DESCRIPTION OF THE SKIRTLESS EMBODIMENT OF FIGS. 10 AND 11 Referring now to FIGS. 10 and 11, there are shown different views of a modified form of the round folding shoe of FIGS. 7-9 wherein most of the skirt portion of the folding shoe is omitted. More particularly, there is shown a folding shoe 70 having a tubular member 71 and a spaced apart guide member 72, both of which are mounted on and carried by a support plate 73. The tubular member 71 includes an inclined throat 74 for providing the desired folding action. The spaced-apart guide member 72 corresponds to that portion of the skirt member which includes and lies below the lower tail surface of the earlier embodiments. In other words, the length B and the peak height .I of the inclined upper surface of the guide member 72 of FIGS. 10 and 11 are determined by the same relationships as given above for the earlier embodiments. The shape of the throat line 74 is also determined in the same manner as for the throat lines of the earlier embodiments. The distance from the far (left-hand) edge of the guide member 72 to the near (left-hand) edge of the throat 74, as measured along a horizontal line, is equal to G, where G is determined in the same manner as previously considered.

This skirtless embodiment of FIGS. 10 and 11 is particularly easy to fabricate. The appropriate patterns for the tubular member 71 and the guide member 72 are cut from flat sheet metal stock, folded and mounted on the support plate 73. The folding, in this case, is more easily accomplished.

It should be noted that this skirtless fabrication technique can be used with any of the round, obround, or flat embodiments considered herein.

DESCRIPTION OF THE TUBELESS EMBODIMENT OF FIG. 12.

Referring now to FIG. 12, there is shown a folding shoe wherein the vertically extending tubular member of the earlier embodiments has been omitted. The particular example shown in FIG. 12 corresponds to the obround embodiment of FIG. 2 with the FIG. 2 tubular member 21 omitted. Thus, the folding shoe 80 of FIG. 12 includes only a skirt member 81. This skirt member 81 includes a lower tail surface 82, an upper tail surface 83, an inclined and downwardly curving throat 84, a pair of flat side surfaces, and a pair of curved shoulder surfaces, the latter items of which are not visible in the cross-sectional view of FIG. 12. The dimensions for the various parts of the skirt member 81 are determined by the same relationships as set forth above for the other embodiments. Also, this tubeless fabrication technique can be used with any of the round, obround, or flat embodiments considered herein.

DESCRIPTION OF THE FLAT EMBODIMENT OF FIGS. 13 AND 14 FIGS. 13 and 14 show unfolded and folded views of a folding shoe for use in folding flexible sheet material into a tube of flat shape. In terms of the basic relationship W=1rr+F (II), the present embodiment represents the case where the 'rrr factor is allowed to approach zero. In such case, for all practical purposes, W becomes equal to F. The various dimensional relationships set forth above for the obround embodiment apply equally well to the present flat embodiment with the observation that some of such relationships can be simplified by assuming that W is equal to F. Also, it is noted that the parameter N, denoting the distance between the X axis coordinates L2 and L3 (also L4 and L5), goes to zero.

As indicated in FIGS. 13 and 14, the folding shoe 90 includes a flat tail surface 91 of trapezoidal shape for receiving the sheet material 92 (FIG. 14) and guiding it from the longer to the shorter of the two parallel edges 93 and 94 thereof. The longer edge 93 constitutes a base edge or leading edge, while the shorter edge 94 constitutes a top edge. The folding shoe 90 also includes a pair of flat side surfaces 95 and 96 extending from the two nonparallel edges 97 and 98, respectively, of the tail surface 91 in a direction toward and perpendicular to a horizontal reference plane passing through the base edge 93 of the tail surface 91. Second edges 99 and 100 of the side surfaces 95 and 96 lie on lines perpendicular to the horizontal reference plane and passing through the end points at the two ends of the top edge 94 of the tail surface 91.

The folding shoe 90 further includes a pair of flat throatforming surfaces 101 and 102 extending from the second edges 99 and 100, respectively, of the side surfaces 95 and 96, respectively, inwardly toward a perpendicular line passing through the midpoint of the top edge 94 of the tail surface 91. Such throat-forming surfaces 101 and 102 lie parallel to the top edge 94 and include upper edges 103 and 104, respectively, which lie at an oblique angle with respect to such top edge 94 and run toward the two end points of such top edge 94. The oblique or inclined edges I03 and I04 and the top edge 94 constitute the throat of the folding shoe 90.

The folding shoe 90 further includes a vertically extending tubular member formed by surfaces 105, 106, and 107 (FIG. 13) after the flat sheet metal piece of FIG. 13 is folded to the final shape indicated in FIG. 14. A folded portion of the flexible packaging material, as it emerges from the lower end of such tubular member, is indicated at 92a.

GENERAL While the foregoing embodiments have been described in terms of laying out a pattern on a flat piece of sheet metal and then folding the sheet metal to obtain the desired folding shoe, it should be clearly understood that the present invention, in its broader aspects, is not limited to this particular manner of fabrication. For example, another way of fabricating the folding shoe would be to cut the various shoe parts from separate pieces of metal and then soldering them together in the appropriate manner. A further way of fabricating the folding shoes of the present invention would be to use a folded sheet metal shoe as a master pattern and then to prepare therefrom a molding cast which could thereafter be used to fabricate additional shoes by metal casting them in such mold.

The choice of which shape of folding shoe (round, obround, or flat) to use in any particular application will depend upon the size and shape of the product to be packaged.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising:

a guide surface for initially receiving the sheet material and guiding it in a first direction;

and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction, at least a portion of such throat being inclined relative to this second direction with the length of the throat, as measured along an axis running parallel to the second direction, being equal to Ti0.09 inches where T is defined by the relationship:

T=0.738W0.238F

where W is the width of the tube when pressed flat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

2. A folding shoe in accordance with claim 1 wherein the guide surface is a flat surface.

3. A folding shoe in accordance with claim 2 wherein the flat guide surface has a leading edge which is perpendicular to .the direction of movement of the sheet material and has side edges which form acute angles with respect to this leading edge, the width of the leading edge being equal to the width of the sheet material to be folded.

4. A folding shoe in accordance with claim 1 wherein the more upstream part of the throat is nearer the guide surface and the throat means is split and overlapped on the side thereof which is farther from the guide surface, the overlapped parts being separated by a small gap for enabling the passage of sheet material therebetween.

5. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising:

a guide surface for initially receiving the sheet material and guiding it in a first direction; and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction;

the distance from the far edge of the guide surface to the near edge of the throat, as measured along a line running perpendicular to the second direction, being equal to Oil 0% where G is defined by the relationship:

where Wis the width of the tube when prermed llut, I. in the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

6. A folding shoe in accordance with claim 5 wherein the guide surface is a flat surface.

7. A folding shoe in accordance with claim 6 wherein the flat guide surface has a leading edge which is perpendicular to the direction of movement of the sheet material and has side edges which form acute angles with respect to this leading edge, the width of the leading edge being equal to the width of the sheet material to be folded.

8. A folding shoe in accordance with claim 5 wherein at least a portion of the throat is inclined relative to the second direction and the more upstream part of the throat is nearer the guide surface and the throat means is split and overlapped on the side thereof which is farther from the guide surface, the overlapped parts being separated by a small gap for enabling the passage of sheet material therebetween.

9. A folding shoe in accordance with claim 5 wherein at least a portion of the throat is inclined relative to the second direction and the length of the throat, as measured along an axis running parallel to the second direction, is equal to Ti0.09 inches where T is defined by the relationship:

T=0.738W0.238F. 10. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising:

a guide surface for initially receiving the sheet material and guiding it in a first direction; A

and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction;

the length of the initial guide surface in the direction of movement of the sheet material thereover being equal to Btl0% where B is defined by the relationship:

B=l .505(L+F) where L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat-sided portion of the tube as it leaves the throat.

11. A folding shoe in accordance with claim 10 wherein the guide surface is a flat surface.

12. A folding shoe in accordance with claim 11 wherein the flat guide surface has a leading edge which is perpendicular to the direction of movement of the sheet material and has side edges which fonn acute angles with respect to such leading edge, the width of the leading edge being equal to the width of the sheet material to be folded.

13. A folding shoe in accordance with claim 10 wherein the initial guide surface is a flat surface of trapezoidal shape lying at a first angle with respect to the second direction, the longer of the two parallel edges being the leading edge and lying at right angles to the direction of movement of the sheet material and wherein the folding shoe further includes a second flat guide surface of trapezoidal shape lying at a second angle with respect to the second direction, the longer of the two parallel edges thereof joining the shorter parallel edge of the initial guide surface and the shorter parallel edge of the second guide surface joining the throat of the throat means.

14. A folding shoe in accordance with claim 13 wherein the length of the second guide surface in the direction of movement of the sheet material thereover is equal to (IL-10% where Q is defined by the relationship:

where Wis the width of the tube when pressed flat.

15. A folding shoe in accordance with claim 14 wherein the acute angle between the initial guide surface and the second direction is equal to 64 35 i2 and the acute angle between the second guide surface and the second direction is equal to 54 13' :2.

16. A folding shoe in accordance with claim wherein at 17. A folding shoe in accordance with claim 10 wherein at least a portion of the throat is inclined relative to the second direction and the length of the throat, as measured along an axis running parallel to the second direction, is equal to Till09 inches where T is defined by the relationship:

where W is the width of the tube when pressed flat.

18. A folding shoe in accordance with claim 10 wherein the distance from the far edge of the guide surface to the near edge of the throat, as measured along a line running perpendicular to the second direction, is equal to G:l0% where G is defined by the relationship:

where W is the width of the tube when pressed flat 19. A folding shoe in accordance with claim 18 wherein at least a portion of the throat is inclined relative to the second direction and the length of the throat, as measured along an axis running parallel to the second direction, is equal to T2009 inches where T is defined by the relationship:

T=0.738W0i238F 20. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising: i

a guide surface for initially receiving the sheet material and guiding it in a first direction;

and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction, at least a portion of such throat being inclined relative to this second direction and the throat being shaped such that if the throat means is split at the low point of the throat and unfolded so that the throat line lies in a single plane, such throat line would describe an arched line extending from and returning to a base line passing through the end points of such throat line with such arched line being symmetrical about a line perpendicular to the base line and passing through the midpoint of the arched line with such arched line including linear segments extending upwardly from the base line and inclined inwardly towards the midpoint and at angles of with respect to the base line and parabolic segments extending from the upper ends of the linear segments and curving inwardly toward the midpoint.

21. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising:

a guide surface for initially receiving the sheet material and guiding it in a first direction;

and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction, at least a portion of such throat being inclined relative to this second direction and the throat being shaped such that if the throat means is split at the low point of the throat and unfolded so that the throat line lies in a single plane, such throat line would describe an arched line extending from and returning to a base line passing through the end points of such throat line with the relationship:

0.803 (X- 0.5F) Y= W +0.738W0.238F

where X is the distance between the point in question and the midpoint of the arched line, as measured along a line parallel to the baseline, Wis the width of the tube when pressed flat, and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

22. A folding shoe in accordance with claim 21 wherein the linear segments are inclined at angles of 45 with respect to the baseline.

23. A folding shoe in accordance with claim 20 wherein the arched line includes a linear segment located intermediate and joining the upper ends of the parabolic segments and lying parallel to the baseline.

24. A folding shoe in accordance with claim 23 wherein the intermediate linear segment lies at a distance of Ti0.09 inches from the baseline where T is defined by the relationship:

T=0.738W-0.238F and wherein each point on each parabolic segment lies at a distance of Yi0.09 inches from the baseline where Y is defined by the relationship:

where X is the distance between the point in question and the midpoint of the arched line, as measured along a line parallel to the baseline, W is the width of the tube when pressed flat, and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

25. A folding shoe in accordance with claim 24 wherein the linear segments extending from the baseline are inclined at angles of 45 with respect to the baseline.

26. A folding shoe for use in folding flexible sheet material into a tube of round or obround shape comprising:

tubular means having the opening at one end thereof inclined relative to the longitudinal center axis of such tubular means for providing a throat for receiving and folding the sheet material;

and skirt means for guiding the sheet material to the throat,

such skirt means at least partially surrounding the tubular means and including a first flat tail surface joined to the outermost longitudinal extremity of the throat end of the tubular means and extending outwardly from the tubular means and inclined at a first angle with respect to the longitudinal axis thereof, a second flat tail surface joined to the outer extremity of the first tail surface and extending outwardly from the tubular means and inclined at a second angle with respect to the longitudinal axis thereof, a pair of flat side surfaces running from the side edges of the second tail surface to the tubular means, the planes of such flat side surfaces being parallel to the longitudinal axis of the tubular means and tangent to the curvature of the tubular means along the lines of contact therewith and a pair of curved shoulder surfaces extending over the areas bounded by the two flat side surfaces, the side edges of the first tail surface and the throat of the tubular means.

27. A folding shoe in accordance with claim 26 wherein the tubular means and any overlying portion of the skirt means is split and overlapped on the side thereof which is farther from the first flat tail surface, the overlapped parts being separated by a small gap for enabling the passage of sheet material therebetween.

28. A folding shoe in accordance with claim 26 wherein the acute angle between the first flat tail surface and the longitudinal axis of the tubular means is equal to 54 13' i2 and the acute angle between the second flat tail surface and the longitudinal axis is equal to 64 35 fl".

29. A folding shoe in accordance with claim 26 wherein the length of the throat, as measured along an axis running parallel to the longitudinal center axis of the tubular means is equal to Ti0.09 inches where T is defined by the relationship:

T=0.738W0.238F where W is the width of the tube when pressed flat and F is the width of any flat sided portion of the unpressed tube as it leaves the throat.

30. A folding shoe in accordance with claim 26 wherein the distance from the far edge of the second flat tail surface and the near edge of the throat, as measured along a line running perpendicular to the longitudinal center axis of the tubular means, is equal to Gil% where G is defined by the relationship:

G=l.024W+l.036L-l-0.0l3F where W is the width of the tube when pressed flat, L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

31. A folding shoe in accordance with claim 26 wherein the length of the first flat tail surface in the direction of movement of the sheet material thereover is equal to Qil0% where Q is defined by the relationship:

Q=1.262( WF) and the length of the second flat tail surface in the direction of movement of the sheet material thereover is equal to Bil0% where B is defined by the relationship: B=l.505(L+F) where W is the width of the tube when pressed flat, L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

32. A folding shoe in accordance with claim 26 wherein the throat is shaped such that if the tubular means is split at the low point of the throat and unfolded so that the throat line lies in a single plane, such throat line would describe an arched line extending from and returning to a baseline passing through the end points of such throat line with such arched line being symmetrical about a line perpendicular to the baseline and passing through the midpoint of the arched line with such arched line including linear segments extending upwardly from the baseline and inclined inwardly toward the midpoint and parabolic segments extending form the upper ends of the linear segments and curving inwardly toward the midpoint.

33. A folding shoe in accordance with claim 32 wherein each point on each parabolic segment lies at a distance of Yi0.09 inches from the baseline where Y is defined by the relationship:

where X is the distance between the point in question and the midpoint of the arched line, as measured along a line parallel to the baseline, W is the width of the tube when pressed flat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

34. A folding shoe for use in folding flexible sheet material into a tube of round or obround shape comprising:

support means;

a guide member carried by the support means and having a flat guide surface for initially receiving the sheet material and guiding it in a first direction;

and a tubular member carried by the support means and spaced apart from the guide member, such tubular means having the opening at one end thereof inclined relative to the longitudinal axis thereof for providing a throat for receiving the sheet material from the guide surface, folding it and guiding it into the tubular member, the flat guide surface lying at an oblique angle with respect to the longitudinal axis of the tubular member and the part of the throat nearest the flat guide surface being the part located at the outermost longitudinal extremity of the throat end of the tubular member and with the distance from the far edge of the flat guide surface to the near edge of the throat, as measured along a line running perpendicular to the longitudinal axis of the tubular member being equal to G- '-l0% where G is defined by the relationship:

where W is the width of the tube when pressed flat, L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.

35. A folding shoe for use in folding flexible sheet material into a tube of flat shape comprising:

a flat tail surface of trapezoidal shape for receiving the sheet material and guiding it from the longer to the shorter of the two parallel edges thereof, the longer of such parallel edges hereinafter being referred to as the base edge, the shorter being referred to as the top edge, such tail surface extending at an oblique angle relative to a reference plane passing through the base edge;

a pair of flat side surfaces extending from the two nonparallel edges of the tail surface in a direction toward and perpendicular to the reference plane, a second edge of each such side surface lying on a line perpendicular to the reference plane and passing through the end point at its end of the top edge of the tail surface;

and a pair of flat throat-forming surfaces extending from the second edges of the side surfaces inwardly toward a perpendicular line passing through the middle of the top edge of the tail surface, such throat-forming surfaces being parallel to such top edge and perpendicular to the reference plane and each such throat-forming surface having an upper edge lying at an oblique angle with respect to such top edge and running toward the end point at its end of such top edge.

jaw-.0; l lo. 3,636, 826

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Column 4,

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Column 4, pieces-.

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Dated January 76 I077 BURLIE R, BOWEN ET AL line 35,

line 55,

lines 65 lines 16 line 47,

line 19,

lines 24 line 25,

Signed and (SEAL) Attest:

EDWARD I'-I.FLETCHER,JR. Attesting Officer in above-identified patent corrected as show; below:

on" to and 67, change "frontpieces" to -front I and 21, change "r" to "r"-.

change "9,5L" to --O.5L--.

change "W-F" to -WO.l4308F-..

and 25, cancel O 25"25 0 on the left-hand side, insert O? 25"25'.

sealed this 29th day of August 1972.

ROBERT GOTTSCHALK Commissioner of Patents 

1. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising: a guide surface for initially receiving the sheet material and guiding it in a first direction; and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction, at least a portion of such throat being inclined relative to this second direction with the length of the throat, as measured along an axis running parallel to the second direction, being equal to T + OR - 0.09 inches where T is defined by the relationship: T 0.738W-0.238F where W is the width of the tube when pressed flat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.
 2. A folding shoe in accordance with claim 1 wherein the guide surface is a flat surface.
 3. A folding shoe in accordance with claim 2 wherein the flat guide surface has a leading edge which is perpendicular to the direction of movement of the sheet material and has side edges which form acute angles with respect to this leading edge, the width of the leading edge being equal to the width of the sheet material to be folded.
 4. A folding shoe in accordance with claim 1 wherein the more upstream part of the throat is nearer the guide surface and the throat means is split and overlapped on the side thereof which is farther from the guide surface, the overlapped parts being separated by a small gap for enabling the passage of sheet material therebetween.
 5. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising: a guide surface for initially receiving the sheet material and guiding it in a first direction; and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction; the distance from the far edge of the guide surface to the near edge of the throat, as measured along a line running perpendicular to tHe second direction, being equal to G + or -10% where G is defined by the relationship: G 1.024W+1.036L+0.013F where W is the width of the tube when pressed flat, L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.
 6. A folding shoe in accordance with claim 5 wherein the guide surface is a flat surface.
 7. A folding shoe in accordance with claim 6 wherein the flat guide surface has a leading edge which is perpendicular to the direction of movement of the sheet material and has side edges which form acute angles with respect to this leading edge, the width of the leading edge being equal to the width of the sheet material to be folded.
 8. A folding shoe in accordance with claim 5 wherein at least a portion of the throat is inclined relative to the second direction and the more upstream part of the throat is nearer the guide surface and the throat means is split and overlapped on the side thereof which is farther from the guide surface, the overlapped parts being separated by a small gap for enabling the passage of sheet material therebetween.
 9. A folding shoe in accordance with claim 5 wherein at least a portion of the throat is inclined relative to the second direction and the length of the throat, as measured along an axis running parallel to the second direction, is equal to T + or -0.09 inches where T is defined by the relationship: T 0.738W-0.238F.
 10. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising: a guide surface for initially receiving the sheet material and guiding it in a first direction; and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction; the length of the initial guide surface in the direction of movement of the sheet material thereover being equal to B + or - 10% where B is defined by the relationship: B 1.505(L+F) where L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat sided portion of the tube as it leaves the throat.
 11. A folding shoe in accordance with claim 10 wherein the guide surface is a flat surface.
 12. A folding shoe in accordance with claim 11 wherein the flat guide surface has a leading edge which is perpendicular to the direction of movement of the sheet material and has side edges which form acute angles with respect to such leading edge, the width of the leading edge being equal to the width of the sheet material to be folded.
 13. A folding shoe in accordance with claim 10 wherein the initial guide surface is a flat surface of trapezoidal shape lying at a first angle with respect to the second direction, the longer of the two parallel edges being the leading edge and lying at right angles to the direction of movement of the sheet material and wherein the folding shoe further includes a second flat guide surface of trapezoidal shape lying at a second angle with respect to the second direction, the longer of the two parallel edges thereof joining the shorter parallel edge of the initial guide surface and the shorter parallel edge of the second guide surface joining the throat of the throat means.
 14. A folding shoe in accordance with claim 13 wherein the length of the second guide surface in the direction of movement of the sheet material thereover is equal to Q + or - 10% where Q is defined by the relationship: Q 1.262(W-F) where W is the width of the tube when pressed flat.
 15. A folding shoe in accordance with claim 14 wherein the acute angle between the initial guide surface and the second direction is equal to 64* 35'' + or - 2* and the acute angle between tHe second guide surface and the second direction is equal to 54* 13'' + or - 2* .
 16. A folding shoe in accordance with claim 10 wherein at least a portion of the throat is inclined relative to the second direction and the more upstream part of the throat is nearer the guide surface and the throat means is split and overlapped on the side thereof which is farther from the guide surface, the overlapped parts being separated by a small gap for enabling the passage of sheet material therebetween.
 17. A folding shoe in accordance with claim 10 wherein at least a portion of the throat is inclined relative to the second direction and the length of the throat, as measured along an axis running parallel to the second direction, is equal to T + or -0.09 inches where T is defined by the relationship: T 0.738W-0.238F where W is the width of the tube when pressed flat.
 18. A folding shoe in accordance with claim 10 wherein the distance from the far edge of the guide surface to the near edge of the throat, as measured along a line running perpendicular to the second direction, is equal to G + or - 10% where G is defined by the relationship: G 1.024W+1.036L+0.013F where W is the width of the tube when pressed flat.
 19. A folding shoe in accordance with claim 18 wherein at least a portion of the throat is inclined relative to the second direction and the length of the throat, as measured along an axis running parallel to the second direction, is equal to T + or -0.09 inches where T is defined by the relationship: T 0.738W-0.238F
 20. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising: a guide surface for initially receiving the sheet material and guiding it in a first direction; and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction, at least a portion of such throat being inclined relative to this second direction and the throat being shaped such that if the throat means is split at the low point of the throat and unfolded so that the throat line lies in a single plane, such throat line would describe an arched line extending from and returning to a base line passing through the end points of such throat line with such arched line being symmetrical about a line perpendicular to the base line and passing through the midpoint of the arched line with such arched line including linear segments extending upwardly from the base line and inclined inwardly towards the midpoint and at angles of 45* with respect to the base line and parabolic segments extending from the upper ends of the linear segments and curving inwardly toward the midpoint.
 21. A folding shoe for use in folding flexible sheet material into a tube of round, obround or flat shape comprising: a guide surface for initially receiving the sheet material and guiding it in a first direction; and means having a throat for receiving the sheet material from the guide surface, folding it and guiding it in a second direction, at least a portion of such throat being inclined relative to this second direction and the throat being shaped such that if the throat means is split at the low point of the throat and unfolded so that the throat line lies in a single plane, such throat line would describe an arched line extending from and returning to a base line passing through the end points of such throat line with such arched line being symmetrical about a line perpendicular to the base line and passing through the midpoint of the arched line with such arched line including linear segments extending upwardly from the base line and inclined inwardly towards the midpoint and parabolic segments extending from the upper ends of the linear segments and curving inwardly toward the midpoint with each point on each parabolic segmenT lying at a distance of Y + or -0.09 inches from the base line where Y is defined by the relationship: where X is the distance between the point in question and the midpoint of the arched line, as measured along a line parallel to the base line. W is the width of the tube when pressed flat, and F is the width of any flat sided portion of the unpressed tube as it leaves the throat.
 22. A folding shoe in accordance with claim 21 wherein the linear segments are inclined at angles of 45* with respect to the baseline.
 23. A folding shoe in accordance with claim 20 wherein the arched line includes a linear segment located intermediate and joining the upper ends of the parabolic segments and lying parallel to the base line.
 24. A folding shoe in accordance with claim 23 wherein the intermediate linear segment lies at a distance of T + or - 0.09 inches from the baseline where T is defined by the relationship: T 0.738W-0.238F and wherein each point on each parabolic segment lies at a distance of Y + or - 0.09 inches from the baseline where Y is defined by the relationship: where X is the distance between the point in question and the midpoint of the arched line, as measured along a line parallel to the base line, W is the width of the tube when pressed flat, and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.
 25. A folding shoe in accordance with claim 24 wherein the linear segments extending from the base line are inclined at angles of 45* with respect to the base line.
 26. A folding shoe for use in folding flexible sheet material into a tube of round or obround shape comprising: tubular means having the opening at one end thereof inclined relative to the longitudinal center axis of such tubular means for providing a throat for receiving and folding the sheet material; and skirt means for guiding the sheet material to the throat, such skirt means at least partially surrounding the tubular means and including a first flat tail surface joined to the outermost longitudinal extremity of the throat end of the tubular means and extending outwardly from the tubular means and inclined at a first angle with respect to the longitudinal axis thereof, a second flat tail surface joined to the outer extremity of the first tail surface and extending outwardly from the tubular means and inclined at a second angle with respect to the longitudinal axis thereof, a pair of flat side surfaces running from the side edges of the second tail surface to the tubular means, the planes of such flat side surfaces being parallel to the longitudinal axis of the tubular means and tangent to the curvature of the tubular means along the lines of contact therewith and a pair of curved shoulder surfaces extending over the areas bounded by the two flat side surfaces, the side edges of the first tail surface and the throat of the tubular means.
 27. A folding shoe in accordance with claim 26 wherein the tubular means and any overlying portion of the skirt means is split and overlapped on the side thereof which is farther from the first flat tail surface, the overlapped parts being separated by a small gap for enabling the passage of sheet material therebetween.
 28. A folding shoe in accordance with claim 26 wherein the acute angle between the first flat tail surface and the longitudinal axis of the tubular means is equal to 54* 13'' + or - 2* and the acute angle between the second flat tail surface and the longitudinal axis is equal to 64* 35'' + or - 2* .
 29. A folding shoe in accordance with claim 26 wherein the length of the throat, as measured along an axis running parallel to the longitudinal center axis of the tubular means is equal to T + or - 0.09 inches where T is defined by the relationship: T 0.738W-0.238F wHere W is the width of the tube when pressed flat and F is the width of any flat sided portion of the unpressed tube as it leaves the throat.
 30. A folding shoe in accordance with claim 26 wherein the distance from the far edge of the second flat tail surface and the near edge of the throat, as measured along a line running perpendicular to the longitudinal center axis of the tubular means, is equal to G + or - 10% where G is defined by the relationship: G 1.024W+1.036L+0.013F where W is the width of the tube when pressed flat, L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.
 31. A folding shoe in accordance with claim 26 wherein the length of the first flat tail surface in the direction of movement of the sheet material thereover is equal to Q + or - 10% where Q is defined by the relationship: Q 1.262(W-F) and the length of the second flat tail surface in the direction of movement of the sheet material thereover is equal to B + or - 10% where B is defined by the relationship: B 1.505(L+F) where W is the width of the tube when pressed flat, L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat sided portion of the unpressed tube as it leaves the throat.
 32. A folding shoe in accordance with claim 26 wherein the throat is shaped such that if the tubular means is split at the low point of the throat and unfolded so that the throat line lies in a single plane, such throat line would describe an arched line extending from and returning to a baseline passing through the end points of such throat line with such arched line being symmetrical about a line perpendicular to the baseline and passing through the midpoint of the arched line with such arched line including linear segments extending upwardly from the baseline and inclined inwardly toward the midpoint and parabolic segments extending form the upper ends of the linear segments and curving inwardly toward the midpoint.
 33. A folding shoe in accordance with claim 32 wherein each point on each parabolic segment lies at a distance of Y + or -0.09 inches from the baseline where Y is defined by the relationship: where X is the distance between the point in question and the midpoint of the arched line, as measured along a line parallel to the base line, W is the width of the tube when pressed flat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.
 34. A folding shoe for use in folding flexible sheet material into a tube of round or obround shape comprising: support means; a guide member carried by the support means and having a flat guide surface for initially receiving the sheet material and guiding it in a first direction; and a tubular member carried by the support means and spaced apart from the guide member, such tubular means having the opening at one end thereof inclined relative to the longitudinal axis thereof for providing a throat for receiving the sheet material from the guide surface, folding it and guiding it into the tubular member, the flat guide surface lying at an oblique angle with respect to the longitudinal axis of the tubular member and the part of the throat nearest the flat guide surface being the part located at the outermost longitudinal extremity of the throat end of the tubular member and with the distance from the far edge of the flat guide surface to the near edge of the throat, as measured along a line running perpendicular to the longitudinal axis of the tubular member being equal to G + or - 10% where G is defined by the relationship: G 1.024W+1.036L+0.013F where W is thE width of the tube when pressed flat, L is the width of the overlap of the sheet material as the tube leaves the throat and F is the width of any flat-sided portion of the unpressed tube as it leaves the throat.
 35. A folding shoe for use in folding flexible sheet material into a tube of flat shape comprising: a flat tail surface of trapezoidal shape for receiving the sheet material and guiding it from the longer to the shorter of the two parallel edges thereof, the longer of such parallel edges hereinafter being referred to as the base edge, the shorter being referred to as the top edge, such tail surface extending at an oblique angle relative to a reference plane passing through the base edge; a pair of flat side surfaces extending from the two nonparallel edges of the tail surface in a direction toward and perpendicular to the reference plane, a second edge of each such side surface lying on a line perpendicular to the reference plane and passing through the end point at its end of the top edge of the tail surface; and a pair of flat throat-forming surfaces extending from the second edges of the side surfaces inwardly toward a perpendicular line passing through the middle of the top edge of the tail surface, such throat-forming surfaces being parallel to such top edge and perpendicular to the reference plane and each such throat-forming surface having an upper edge lying at an oblique angle with respect to such top edge and running toward the end point at its end of such top edge. 